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.Dd June 15, 2023
.Dt SYSCALL_MODULE 9
.Os
.Sh NAME
.Nm SYSCALL_MODULE
.Nd syscall kernel module declaration macro
.Sh SYNOPSIS
.In sys/param.h
.In sys/kernel.h
.In sys/proc.h
.In sys/module.h
.In sys/sysent.h
.Fn SYSCALL_MODULE name "int *offset" "struct sysent *new_sysent" "modeventhand_t evh" "void *arg"
.Sh DESCRIPTION
The
.Fn SYSCALL_MODULE
macro declares a new syscall.
.Fn SYSCALL_MODULE
expands into a kernel module declaration with name
.Ql sys/ Ns Fa name .
.Pp
The rest of the arguments expected by this macro are:
.Bl -tag -width ".Fa new_sysent"
.It Fa offset
A pointer to an
.Vt int
which saves the offset in
.Vt "struct sysent"
where the syscall is allocated.
If the location pointed to by
.Fa offset
holds a non 0 number it will be used if possible.
If it holds 0 then one will be assigned.
.It Fa new_sysent
is a pointer to a structure that specifies the function implementing
the syscall and the number of arguments this function needs (see
.In sys/sysent.h ) .
.It Fa evh
A pointer to the kernel module event handler function with the argument
.Fa arg .
Please refer to
.Xr module 9
for more information.
.It Fa arg
The argument passed to the callback functions of the
.Fa evh
event handler when it is called.
.El
.Pp
The syscall number assigned to the module can be retrieved using the
.Xr modstat 2
and
.Xr modfind 2
system calls.
The MACRO
.Fn SYSCALL_MODULE_HELPER
includes
.Fn SYSCALL_MODULE
and much of its boilerplate code.
.Sh EXAMPLES
A minimal example for a syscall module can be found in
.Pa /usr/share/examples/kld/syscall/module/syscall.c .
.Sh SEE ALSO
.Xr module 9
.Pp
.Pa /usr/share/examples/kld/syscall/module/syscall.c
.Sh AUTHORS
This manual page was written by
.An Alexander Langer Aq Mt alex@FreeBSD.org .
